I want to build a wicked one box for 2 18' subs. I wanted to know if I can still use the 2", 4", and 8" rule to build the horn, but instead of using the 36" by 36" dimensions, can I use th space in my vehicle, which is 44" by 44"? Or what other method do you would be recommended to build this box using 2 18" subs?

I guess it will perform at least as good, if not, better.The only problem might be the width of throat and how to re-calculate that.Also, it would be much heavier, since you will need to brace it very well or use thicker panels.

I would start by cutting a piece of mdf 44" x 44" if that will fit in your space. Next lay out the 36" x 36" design in the middle of the mdf. Keep the throat (most narrow part of the horn) the same but add the height needed to accommodate the 18"s. The inside angled pieces that go from front to back will need to be extend about 3" to 4" to deal with the extra size. The trick will be the port part of the enclosure, this board will need to be angled a little different and bigger/longer. Keep the port the standard size except for height. This will be a trial and error build so cut everything big to start with, that way you can cut it down if need. My two cents if you would like more info let me know.

I am currently building a wo box for 2 15" that are about 7" deep with an 10" dia magnet and it BARELY fits in a 48" wide wo box with about 2cu ft sealed chamber. The baffle ended up being like 18" with that setup....and with 18s I would assume you'd want at least 22" or so...so at least a 5' wide box?!?!but here is a cadd of the box with 2 15s with the depths of the drivers and magnets with a 48"x36" design.